There is an increasing need for variable adjustment possibilities in order to adapt the backrest configuration, in particular its width, to the individual requirements of a particular wheelchair user. The requirements can occur from the need of comfort of the user or from the need of accommodation of a variety of health issues and reasons for wheelchair use.
Document U.S. Pat. No. 2,534,009 describes a conventional adjustable backrest, which comprises a pair of spaced apart side bars, each side bar having a plurality of spaced transverse bars extending therefrom towards the opposite side bar. The transverse bars of the two side bars comprise each a circular through hole and a slot. Fasteners pass through corresponding hole and slot in order to fasten the transverse bars together, the holes and slots being positioned so that the lateral spacing of the side bars is adjustable. According to this embodiment, the width adjustment of the backrest depends on the lengths of the slots, nevertheless the side bars do not contribute itself to the width adjustment and therefore limit the width adjustment. Moreover, the transverse bars of each side bar are not linked together so that the reliability of the assembly depends essentially on the connection means between the side bars and their transverse bars.
Document U.S. Pat. No. 5,564,786 describes an adjustable seat frame. The frame comprises a pair of spaced apart side rail having a plurality of spaced parallel transverse beams extending therefrom towards the opposite rail and a central beam telescopingly engaged between corresponding beams on each rail. Here again, the side rails do not contribute to the width adjustment of the frame and the transverse beams are not linked together. Due to the connections between each central beam and its corresponding transverse beams, this embodiment need two times more fastening means than the embodiment described in U.S. Pat. No. 2,534,009.